Hundreds of NCEA students who asked to see their exam booklets have been sent other people's by mistake.

The revelation that 455 students were sent other people's booklets this year was news to principals, who were not notified about the blunder, although Education Minister Hekia Parata was.

Only 260 students, ranging across all NCEA levels, contacted the Qualifications Authority to say they had the wrong booklets. Of those, 169 were then sent the correct booklets; the other 91 cases remain unresolved.

A subcontractor's computer glitch has been blamed for the error, which NZQA discovered in January.

Tawa College principal Murray Lucas said he was made aware of the error by a student, and was "disappointed" NZQA had not contacted him directly.

"It's a difficult situation for students to deal with, and I'm disappointed to have to hear these things from the students."

Labour's education spokesman Chris Hipkins said NZQA should have been upfront about the botch-up.

"When a breach like this occurs, people should be told about it, and to sweep it under the rug is unacceptable."

He said it was disgraceful that Parata knew about the issues and did not make a public statement or insist schools be notified.

NZQA had addressed Parliament's education and science select committee since it became aware of the error, but did not reveal it. "It's pretty outrageous they haven't given full disclosure about this," Hipkins said.

Parata said she was told about the problems in January, and updated again in February by NZQA.

"While it is a regrettable mistake, I have been assured by NZQA that further quality checks have been put in place to ensure this type of error does not take place in future."

NZQA deputy chief executive of assessment Richard Thornton said the error was not a privacy breach because the exam booklets did not contain any information that could identify a person.

He said the next step would be to contact schools directly.

Hipkins said an organisation of NZQA's size needed to have effective systems in place to pick up these sorts of errors.

A move towards a digital marking system - as proposed by NZQA over the next five years - had even more room for error, and proper checks and security measures needed to be implemented. "This won't give the public a large amount of confidence that they can get it right."

Secondary Principals' Association president Tom Parsons confirmed that principals did not know about the booklets blunder.

Earlier this month, speaking about NZQA's move to digital assessments, Parsons said last year's exams were the first time he could recall when there were not any problems.

Yesterday he said that clean bill of health had been tarnished. "Considering we just finished a secondary principals' conference where not one person raised this with me, I find it frightening and bewildering that it wasn't known about if students were being affected."

NCEA level 3 results determined career paths and halls of residence for students, and getting results right was a "high-stakes game", he said.

Students relying on their exam booklets to contest marking can apply through their schools for special consideration of their results. Thornton said their final result would be based on evidence provided by the school.

But Hipkins said variables in how well students did under exam pressure, and the number of teenagers known to cram at the end of the year, would make special consideration a problem.

WRONG RESULTS CONCERN STUDENTS

Tawa College student Hayley Dibley sat four NCEA level 1 external exams last year - but the exam booklets she got back in January were for a level 3 student.

"I was pretty annoyed because everyone was going through comparing and checking their answers but I couldn't do anything," the 16-year-old, now in year 12, said.

"I was worried that if I didn't get them back, I would miss the chance to get them re-marked if there were any problems with the marking."

The NZQA botch-up has been discussed by students on Facebook and Hayley said she knew of at least one other Tawa College student who was affected.

Her sister returned the exam booklets to NZQA the day after they were received and was told NZQA was not aware the problem had affected anyone else.

"A bit more than two weeks later [the right ones] just arrived. There was no communication before that and no explanation with my books," Hayley said.

"I would have thought I would get an apology at the least."

Tawa College principal Murray Lucas is in contact with NZQA about the problem.